Related Stories

Fish first An unusual prehistoric fish with fins near its bottom has helped to solve the mystery over why most animals, including humans, have paired limbs.

The fish, Euphanerops, is possibly the first creature on the planet to have evolved paired appendages, which in this case were fins.

The 370-million-year-old species is described in the latest issue of Biology Letters.

"Fins are the world's first limb-like appendages," lead author Robert Sansom says. "Paired limbs would subsequently develop from paired fins in the transition from sea to land, but the first evolution of paired appendages was a big, important step in the evolution and development of vertebrates", which are animals with a backbone or spinal column.

Sansom, a researcher at both the University of Manchester and the University of Leicester, and colleagues analysed 36 Euphanerops specimens unearthed in Quebec, Canada. This was a jawless fish that lived long before dinosaurs first emerged.

Many living fish have a single anal fin, located at the centre back of the fish's underside near its rear end. The fin is thought to help maintain control of body position.

Radical point

This ancient fish, however, evolved two such fins. Some subsequent fish did not evolve the paired appendages, so fish with all sorts of fin combinations existed for a while.

"What this research leads us to believe is that, at this early stage (in evolutionary history), vertebrates were trying out lots of different body plans, some familiar, some less familiar, and only some that survived," Sansom says.

The change happened at a radical point in fish history when some of them were starting to evolve jaws and teeth. These attributes likely emerged for reasons similar to fish gaining fins - improved hunting and escape skills.

"The evolution of paired appendages and more sophisticated fins will probably be for improved locomotion, potentially related to an arms race between tracking down prey and avoiding predators," says Sansom.

"Paired fins allow for more sophisticated control of movement."

This movement, which at first just happened underwater, later helped some species make the transition from water to land.